Particle boards are widely used, e.g., in the furniture and construction industry. Typically, particle boards are made from lignocellulosic particles, such as wood chips, strands of wood, splinters, sawdust and/or lignocellulosic fibers, which particles are first admixed (or coated) with a thermally activatable binder. Generally, a mixture of the lignocellulosic particles and binder is prepared and then distributed on a horizontal receiving surface to form a mat. The mat is subsequently pressed under a temperature, sufficiently elevated to activate the binder. When the mat of binder-coated particles is subjected to heating and compression, the binder is activated (i.e., caused to flow and/or set) and binds the particulate material, to form a coherent sheet or board. After the pressing step, the compressed board or sheet is cooled and trimmed, to form the final product. Such processes are generally known.
It is sometimes desirable that the particle board comprises multiple layers. For example, it is known to use a set of rollers for fractionating particles according to size, thereby obtaining a particle board having at its outer surface layers, e.g., a fraction of finer particles, whereas the larger particles are distributed preferentially at the inner (core) layers of the product. Particle boards having a finer fraction of particles at the outer surface are sometimes aesthetically preferred, since they tend to have a smoother outer surface. A smooth outer surface can be advantageous, if a further layer, e.g. a furnace, is to be added to the particle board. Such products are known from U.S. Pat. No. 4,068,991.
In other cases, it is desirable that the larger particles are primarily in the outer surface layers of the board, while the small particles are primarily in the central layer(s) of the board. Such particle boards are also generally known.
The distribution of the particles in various layers, e.g., according to size, has great impact on the mechanical properties of the final product. Large particles at the surface layers of a multi-layer product generally results in a particle board having a higher flexural resistance, as compared to non-layered particle boards.
In order to further improve the mechanical properties of the particle board, it is known to provide oriented layers of elongated particles in so-called oriented strand boards (OSB). Oriented layers of particles increase the flexural resistance of the board, in particular, in the direction of orientation. In OSB boards, the larger particles are normally at the outer layers, and oriented in the longitudinal direction of the board, e.g., in the direction of production, while the smaller particles in the core layers are oriented in the transverse (lateral) direction, or they are not oriented at all. It is known to use disc-rollers for orienting particles in OSB boards, as is described, e.g., in U.S. Pat. No. 7,004,300 and U.S. Pat. No. 4,068,991.
EP 0860255 A1 discloses a procedure and an apparatus for producing OSB boards in which oriented layers of relatively large particles are at the upper and lower surface layers of the board. The relatively small particles are preferentially in the core layers of the board, oriented in the transverse (lateral) direction. EP 0860255 A1 uses a first and a second set of rollers for fractionating the particles according to size, and a third set of rollers, referred to as an “orienting mechanism”, for orienting the particles in the desired direction. In the orienting mechanism, a set of disc-type rollers is used for orienting the larger particles in the lengthwise direction, while relatively smaller particles are oriented in the transverse direction by star-rollers, separated from each other by deflecting plates. This construction comprising two sets of rollers for size fractionation and an additional orienting mechanism does not allow for the production of a particle mat with homogeneously distributed particles in the horizontal and good size separation into vertical layers at very high throughput.
DE 4213928 A1 discloses an apparatus for scattering particles onto a moving belt for forming a particle mat. In one embodiment, a first set of two star-type rollers is used to mix and distribute incoming particles. The two star-type rollers rotate in opposite directions. Particles fall from the two star-type rollers onto two second sets of disc rollers, the two sets rotating in opposite directions. The disc rollers of the second sets separate the particles according to size, such that the larger particles are transported in the laterally outward directions, while smaller particles tend to fall through the disc rollers. The particles fall from the second sets of rollers onto third sets of rollers, which rotate opposite to the rotational direction of the second set of rollers from which they receive the particles, thereby transporting the larger particles laterally inward again. As a result of the rotation of the second and third sets of rollers in opposite directions, a central mixing zone is established in which a mixture of fine and large particles is added to the mat. An efficient separation of the fine and the larger particles is thus not achieved. Furthermore, the construction employing size separation in two opposite directions does not allow for the production of multi-layered mats at very high throughput. Furthermore, the types of rollers used in the first, second and third sets of rollers do not support very high throughput.
DE 10 2010 038 434 A1 discloses an apparatus for producing an oriented strand mat. The apparatus includes three sets of rollers rotating in the same direction. The first set of rollers consists of star-type rollers, and the second set of rollers consists of disc rollers. The choice of rollers in the first and second sets, as well as their spatial orientation relative to each other does not support the production of a particle mat at very high throughput.
Orientation of particles in the upper and lower surface layers of a particle board is not always desirable. In particular, if flexural resistance of a board in all dimensions is desired, orientation of the particles may be disadvantageous. Furthermore, the surface structure of OSB boards is often inferior to the one of non-oriented particle boards. This is of particular relevance in the furniture industry.
The known apparatuses and methods for producing layered, non-oriented particle boards are limited with respect to production speed, homogeneity of the layers, and with respect to the quality of separation of the particles according to size. Methods and apparatuses which are capable of running at a sufficiently high throughput or speed, very often do not fulfill the current needs of the industry with respect of homogeneity and quality of separation according to size. The current invention addresses these needs.
Hence, it is an object of the present invention to provide an apparatus and method for producing a layered, non-oriented mats in a particle board production process, which apparatus or method are capable of producing the mats at very high speed, while still a sufficiently high homogeneity (in the horizontal dimension) and a sufficiently high quality of separation according to size is ascertained in the final product.